Peter Webb
2010-11-09 09:16:29 UTC
|
| >
| >
| >
| >
| >
| > > On Nov 7, 1:37 am, "Peter Webb"
| >
| >
| >
| > > > > Hi.
| >
| > > > > I was thinking about this. Consider a huge disk on a spinner.
| > > > > Suppose
| > > > > we spin it up faster and faster. The outer edge rotates faster
than
| > > > > the inner. Yet this means that at some point, we could have the
| > > > > outer
| > > > > edge going at the speed of light, while the inner edge is going
| > > > > slower! But obviously we can't get it _past_ the speed of light,
of
| > > > > course, so what happens here? My guess is the disk breaks. There
is
| > > > > a
| > > > > "relativistic stress" that builds up as we accelerate the disk,
and
| > > > > it
| > > > > builds up hyperbolically fast, becoming infinitely strong the
moment
| > > > > the outer edge reaches light speed, so at some point before
this,
| > > > > the
| > > > > disk must shatter. Not may, MUST, otherwise we could violate the
| > > > > speed
| > > > > of light limit. It's kind of like how you can't have a rigid
rod.
| >
| > > > > Am I right on this, or totally off base?
| >
| > > > Totally off base. There is no such thing as "Relativistic Stress"
of
| > > > the
| > > > sort you describe.
| >
| > > > Though it is an *excellent* question.
| >
| > >
| > > Hmm. So there is no special "relativistic stress", but what _does_
| > > then happen
| > > to the stress in the (admittedly made of imaginary materials) disk
| > > (how does it
| > > increase/change/etc.) as the outer edge nears the speed of light?
| >
| > if the disc it's all made of the same imaginary material, the logic is
| > that
| > the edges will eject the system in the form of EM waves
| > while the material near the edge will continue to expand
| > outwards.
| >
| > this is figuratively speaking of course because the disc will fragment
| > itself with any real material long before reaching anywhere around c
| >
| > r.y- Hide quoted text -
| >
| > - Show quoted text -
|
| Not necessarily: the centrifugal forces can be made arbitrarily small
| by making the disk arbitrarily large at fixed circumferential speed.
|
| _________________________
| Correct.
|
|
| Thereafter, what happens is a matter for engineering: either the disk
| will fly apart, or it will buckle under differential contraction.
|
| ____________________________
| In this thought experiment, there is no "differential contraction" to
cause
| buckling. A spring whizzing by at 0.9c will be shorter than if measured
in
a
| relatively stationary frame, but this does not mean the spring itself is
| compressed and under tension. These are changes to space and time, not
| changes to the spring per se.
Hmm... let's do the math.
--
"Let there be given a stationary rigid rod; and let its length be L as
measured by a measuring-rod which is also stationary. We now imagine the
axis of the rod lying along the axis of x of the stationary system of
co-ordinates, and that a uniform motion of parallel translation with
velocity v along the axis of x in the direction of increasing x is then
imparted to the rod. We now inquire as to the length of the moving rod" --
Einstein
AND THE ANSWER IS...
xi = (x-vt)/sqrt(1 - v^2/c^2) -- Einstein.
We'll use a 1 metre spring.
xi = 1 / sqrt(1 - 0.9^2/1^2)
= 1 / sqrt( 1 - 0.81)
= 1/ sqrt( 0.19)
= 1 / 0.43588989435406735522369819838596
= 2.2941573387056176590720957809787
A 1 metre spring whizzing by at 0.9c will be 2.3 metres longer
than if measured in a relatively stationary frame.
It will be shorter, not longer, so obviously you have used the wrong| >
| >
| >
| >
| >
| > > On Nov 7, 1:37 am, "Peter Webb"
| >
| >
| >
| > > > > Hi.
| >
| > > > > I was thinking about this. Consider a huge disk on a spinner.
| > > > > Suppose
| > > > > we spin it up faster and faster. The outer edge rotates faster
than
| > > > > the inner. Yet this means that at some point, we could have the
| > > > > outer
| > > > > edge going at the speed of light, while the inner edge is going
| > > > > slower! But obviously we can't get it _past_ the speed of light,
of
| > > > > course, so what happens here? My guess is the disk breaks. There
is
| > > > > a
| > > > > "relativistic stress" that builds up as we accelerate the disk,
and
| > > > > it
| > > > > builds up hyperbolically fast, becoming infinitely strong the
moment
| > > > > the outer edge reaches light speed, so at some point before
this,
| > > > > the
| > > > > disk must shatter. Not may, MUST, otherwise we could violate the
| > > > > speed
| > > > > of light limit. It's kind of like how you can't have a rigid
rod.
| >
| > > > > Am I right on this, or totally off base?
| >
| > > > Totally off base. There is no such thing as "Relativistic Stress"
of
| > > > the
| > > > sort you describe.
| >
| > > > Though it is an *excellent* question.
| >
| > >
http://en.wikipedia.org/wiki/Ehrenfest_paradoxdescribessomethingsimilar.
| >| > > Hmm. So there is no special "relativistic stress", but what _does_
| > > then happen
| > > to the stress in the (admittedly made of imaginary materials) disk
| > > (how does it
| > > increase/change/etc.) as the outer edge nears the speed of light?
| >
| > if the disc it's all made of the same imaginary material, the logic is
| > that
| > the edges will eject the system in the form of EM waves
| > while the material near the edge will continue to expand
| > outwards.
| >
| > this is figuratively speaking of course because the disc will fragment
| > itself with any real material long before reaching anywhere around c
| >
| > r.y- Hide quoted text -
| >
| > - Show quoted text -
|
| Not necessarily: the centrifugal forces can be made arbitrarily small
| by making the disk arbitrarily large at fixed circumferential speed.
|
| _________________________
| Correct.
|
|
| Thereafter, what happens is a matter for engineering: either the disk
| will fly apart, or it will buckle under differential contraction.
|
| ____________________________
| In this thought experiment, there is no "differential contraction" to
cause
| buckling. A spring whizzing by at 0.9c will be shorter than if measured
in
a
| relatively stationary frame, but this does not mean the spring itself is
| compressed and under tension. These are changes to space and time, not
| changes to the spring per se.
Hmm... let's do the math.
--
"Let there be given a stationary rigid rod; and let its length be L as
measured by a measuring-rod which is also stationary. We now imagine the
axis of the rod lying along the axis of x of the stationary system of
co-ordinates, and that a uniform motion of parallel translation with
velocity v along the axis of x in the direction of increasing x is then
imparted to the rod. We now inquire as to the length of the moving rod" --
Einstein
AND THE ANSWER IS...
xi = (x-vt)/sqrt(1 - v^2/c^2) -- Einstein.
We'll use a 1 metre spring.
xi = 1 / sqrt(1 - 0.9^2/1^2)
= 1 / sqrt( 1 - 0.81)
= 1/ sqrt( 0.19)
= 1 / 0.43588989435406735522369819838596
= 2.2941573387056176590720957809787
A 1 metre spring whizzing by at 0.9c will be 2.3 metres longer
than if measured in a relatively stationary frame.
equation.
You should study basic Relativity before trying to answer basic Relativity
questions.
Are there any predictions of relativity that you disagree with, you stupid
cunt?
No.cunt?
Are there any predictions of Relativity that *you* disagree with?